because LA has been making Star Wars games too long and now they all think that the entire human race has the Force and that we can read their minds, so we already know about it.
but on a more realistic note: if they announced it too early, imagine the hype. despite how much i love Blizzard Entertainment, they made that mistake with StarCraft 2 and possibly Diablo 3. id Software has also seemed to have made that mistake with Doom 4.